With the continuing growth in performance of computing technology, the interconnect bandwidth required among microprocessors, memories, and input/output devices continues to increase. Such high speeds create increasing problems for the technology used for interconnections among the microprocessors, memories, and input/output devices. For example, copper trace technology, such as conventionally employed on printed circuit boards, is expected to be limited to 15-20 Gigabits per second as a result of signal degradation, power dissipation, and electromagnetic interference unavoidable at such high clock speeds.
Manufacturers of many electronic products have sought to address the limitations of copper by using more exotic substrates with lower dielectric loss or using more sophisticated input/output equalizers at the transmitter and receiver. Unfortunately all of these potential solutions are costly and power consumptive. Therefore traditional interconnect scaling will no longer satisfy performance requirements. Defining and finding solutions beyond copper and low dielectric loss material will require innovation in design, packaging and unconventional interconnect technology.
One alternative attracting increasing attention is the use of optical interconnect technology. Optical communication technology has been used for many years in long distance applications such as telephony and the internet, and is now sometimes implemented for use in shorter distance applications for the enterprise such as storage area networks and rack-to-rack interconnections. Such optical technology has already demonstrated that at high frequencies, the optical fibers provide longer distance-higher bandwidth capability as compared with electrical cables, yet minimize loss in the transmitted signal.
Unfortunately, optical interconnect technology has associated with it a separate set of implementation difficulties. These difficulties include optical coupling efficiencies, fiber alignment, complex packaging technologies, including hermeticity, thermal management, electrical performance, and manufacturability—the ease of assembly and amenability to automation. Thus, generally speaking, current optical modules or transceivers like SFP, 300 pins MSA, Xenpack, Xpak, X2 and XFP form factors provided by various suppliers including Emcore, Finisar, Agilent, and Bookham are still complex to manufacture and expensive.
Additionally for substantial utility in the computing market, optical transceivers also need (1) extremely low power consumption to compete with electrical solutions, (2) a smaller form factor adapted for and appropriate to the computer industry, and (3) very large interconnect bandwidth to provide data consummate with processing power. One example of a prior art solution is the IBM Terabus project (Exploitation of optical interconnects in future server architectures, Benner et al., 49 IBM J. Res. & Dev. No. 4/5, July./September. 2005). In this concept the transmitter and receiver modules are separate and require a complex structure with multiple chips/modules mounted on a substrate—one module with an array of transmitters and another module with an array of receivers.
A novel solution adapted for computing application to interconnect processing units while increasing communication bandwidth, maintaining an ultra small form factor, decreasing power consumption, simplifying and enabling automated assembly is required.